Nowadays, there are several ways to attach a daughter card perpendicular to a motherboard. These include the following.
1. Removable Edge Card Connector—There are available several removable edge card connector designs where the daughter card such as a memory card, arranged perpendicular to the motherboard, is inserted into a group of pins or contacts that are pre-loaded with a determined amount of force. These contacts are held in place by a molded insulator and hard soldered to the motherboard. The result is a non-soldered, removable interconnect between the memory card or edge card connector and the PCB.
2. Submerged Soldering—Another method of lead attachment comprises inserting the memory card or other PCB with surface mount technology (SMT) pads between two rows of contacts that are held together in a carrier, which is sometimes also referred to as a header. This assembly is fluxed and then submerged into a solder bath up to the SMT pads on the memory card or PCB. This approach results in a permanent soldered interconnect, which, however, requires that the PCB's or memory cards be singulated and put through a secondary process, off-line, which is time-consuming and expensive.
3. Hand Soldering—This attachment method requires a single point solder reflow for each individual contact. An operator would touch a soldering iron and solder wire to make each solder joint. This method is slow and very labor intensive and also requires secondary processing off-line.
4. Screen Print/Solder Bump—In this scheme, during placement of other components on the PCB, solder paste is placed on the SMT pads on the “A” side of a printed circuit board (the terms “A” side and “B” side are meant to designate the two major surfaces of a PCB, with the A side representing the first surface processed and the B side the opposite surface). components are placed onto the paste and then the assembly is reflowed. “Reflowing” is a term of art typically meaning that an assembly is fluxed and then heated to a temperature above the melting point of any solder present causing the solder to penetrate adjacent crevices between solderable electrically-conductive surfaces, typically of copper or a copper alloy, such that upon cooling the solder freezes forming a permanent electrical connection between the electrically-conductive surfaces. The PCB board is then flipped, wet screen paste is applied on the B side, components are placed on the B side, and then a connector for the memory card is placed over the bumps on the A side SMT pads and their leads are placed into the “soft” paste on the SMT pads on the B side, followed by both sides being reflowed. This process does not produce a desirable solder attachment because the leads of the connector are spread when placed over the bumps to the memory card leaving a space or gap between the pin contact region and the SMT pad after reflow.
The problems associated with surface mount soldering a header, especially a long header, to a PCB will be discussed below.